Anisotropic compounds with negative or positive DC-anisotropy and low optical anisotropy

ABSTRACT

Anisotropic compounds with negative or positive DCA and Δn≦0.2 have the formula (1) ##STR1## in which R 1  and R 2  l are independently hydrogen, alkyl, alkoxy having 1 to 12 carbon atoms respectively, or one of R 1  and R 2  can represent cyclical fragment of formulae (1a) or (1b); ##STR2## the bridges Z 1 , Z 2  and Z 3  are identical or different and means covalent bonds or carboxyl or oxycarbonyl groups; R 3  is hydrogen, alkyl or alkoxy group having 1 to 12 carbon atoms, respectively; X 1  and X 4  are independently hydrogen, halogen, nitrile or nitro, wherein at least one of X 1  and X 4  is not hydrogen when R 2  represents a cyclical fragment of formula (1a) or (1b) and Z 2  is a carboxyl group or Z 3  is an oxycarbonyl group, respectively. Liquid crystal compositions are also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to new anisotropic compounds with negative orpositive dielectric constant anisotropy and low, e.g., 0.2 opticalanisotropy (Δn) at the most, as well as liquid crystal (LC) compositionscontaining these anisotropic compounds and are used as the dielectricfor liquid crystal indicators.

2. Description of the Prior Art

The anisotropic compounds known up till now for liquid crystalcompositions whose dielectric constant-anisotropy, abbreviated DCA orΔε, is negative, are mostly of two or three combinations, made up ofaromatic rings with one of two carboxyl groups and, if necessary, acovalent bond as a bridge between the rings, and with one or more sidegroups, i.e., core substituent groups not lying in the molecularlongitudinal axis, such as nitrile or nitro groups, particularly, suchas described in German AS No. 2 240 864, German OS Nos. 2 613 293, 2 835662 and 2 836 086. These known anisotropic compounds with negative DCA(Δε), however, have high viscosity values as well as high values foroptical anisotropy (Δn) (Δε=ε₁₁ -ε.sub.⊥ and Δn=n₁₁ -n.sub.⊥). The DCAof a compound is negative if the dielectric constant (ε) parallel to themolecular axis is smaller than the dielectric constant perpendicular tothe molecular axis. The optical anisotropy (Δn) of a compound ispositive if its refraction index (n₁₉₅) perpendicular to the molecularaxis is smaller than its refraction index (n₁₁) parallel to themolecular axis; this optical anisotropy value, i.e., Δn=n₁₁ -n.sub.⊥ isdesignated "low" here if it is smaller than, or at the most 0.2(Δn≦0.2). Suitable methods for measuring Δn are known in the literature(e.g., I. Haller et al, Mol. Cryst. and Liqu. Cryst. 16/1972/53-59) andusually refer to a definite light wave length (here 633 nm).

It is known from the literature, e.g., German OS No. 2 636 684, that theviscosity of liquid crystalline and linear aromatic compounds with noside groups, such as biphenyl nitriles, can be reduced by substituting acyclohexane ring for one of the phenylene rings. This possibility forproducing anisotropic compounds with high negative DC-anisotropy and lowΔn-values suited for LC compositions has remained unused until now. Tobe sure such compounds with a side group, e.g., methyl or ethyl groupsor chlorine atoms, were mentioned in the German OS No. 2 752 975 among anumber of specially described, linear, tri-cyclic diesters with one ortwo benzol-ring(s) and two or one cyclohexane ring(s); although mentionwas made of the possibility of a side nitrile group, it was notrecognized that a new group of advantageous anisotropic compounds withnegative, not to mention strongly negative, DC-anisotropy would havebeen made accessible according to the structural principle disclosedthere.

Anisotropy, i.e., enantiotropic liquid crystalline or nonotropic orpotentially liquid crystalline compounds with high negativeDC-anisotropy and low Δn-values are required for LC-indicators, as wasdescribed by the applicant in the German PA No. 35 863.6, which utilizethe so-called "inverse Guest-Host-effect"; furthermore, anisotropiccompounds with such characteristics are also required for certain typesof dynamic (scatter/leakage) cells. However, prior known anisotropiccompounds with negative DC anisotropy do not satisfy the requiredconditions or at least not to a satisfactory degree.

A need therefore continues to exist for new anisotropic compounds withnegative DCA and low optical anisotropy (Δn), e.g., for LC-indicatorswith multiplex operation.

SUMMARY OF THE INVENTION

Accordingly, one object of the invention is to provide anisotropiccompounds with negative or positive DCA and low optical anisotropy.

A further object of the invention is to provide liquid crystalcompositions comprising at least one anisotropic compound with negativeor positive DCA and low optical anisotropy.

Briefly, these objects and other objects of the invention as hereinafterwill become more readily apparent can be attained by providing ananisotropic compound of formula (I): ##STR3## in which the side groupsR¹ and R² are hydrogen, C₁ -C₁₂ -alkyl groups or C₁ -C₁₂ -alkoxy groupsand one of the groups R¹ and R² can represent in addition a cyclicalfragment of formula (1a) or (1b); ##STR4## the bridges Z¹, Z² and Z³ areidentical or different and are simple covalent bonds or carboxyl oroxycarbonyl groups; R³ is hydrogen, C₁ -C₁₂ -alkyl or C₁ -C₁₂ alkoxy; atleast one of X¹ to X⁴ and preferably two or more are halogen, nitrile(preferably) or nitro, the remainder being hydrogen. At most one of Z1,Z2 and Z3 is carboxyl or oxycarbonyl with the proviso (A) that at leasttwo of X¹ and X⁴ are not hydrogen when X¹ is nitrile and R¹ is acyclical fragment of formula (1a), (B) at least two of X¹ to X⁴ are nothydrogen when X⁴ is nitrile and R² is a cyclical fragment of formula(1a), and (C) that no benzene ring is directly linked to two oxygenatoms.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention is directed to anisotropic compounds of the formula (1):##STR5## in which the side groups R¹ and R² are hydrogen, C₁ -C₁₂ -alkylgroups or C₁ -C₁₂ -alkoxy groups and one of the groups R¹ and R² canrepresent in addition a cyclical fragment of formula (1a) or (1b);##STR6## the bridges Z¹, Z² and Z³ are identical or different and aresimple covalent bonds or carboxyl or oxycarbonyl groups; R³ is hydrogen,C₁ -C₁₂ -alkyl or C₁ -C₁₂ alkoxy; at least one of X¹ to X⁴ andpreferably two or more are halogen, nitrile (preferably) or nitro, theremainder being hydrogen. At most one of Z1, Z2 and Z3 is carboxyl oroxycarboxyl with the proviso (A) that at least two of X¹ and X⁴ are nothydrogen when X1 is nitrile and R¹ is a cyclical fragment of formula(1a), (B) at least two of X¹ to X⁴ are not hydrogen when X⁴ is nitrileand R² is a cyclical fragment of formula (1a), and (C) that no benzenering is directly linked to two oxygen atoms.

Chlorine is particularly preferred as a halogen, although other halogens(F, Br, I) are acceptable.

It is not necessary that all of X¹ to X⁴ positions be substituted; thus,up to three of the groups X¹ to X⁴, preferably up to two of the groupsX¹ to X⁴ must be halogen, nitro or nitrile (preferably), the remainderbeing hydrogen.

The compounds of formula (1) as in the invention are hereinbelowdesignated as "compounds (1)" for the sake of brevity.

Preferred groups of the "compounds (1)" correspond to the followingformulae (2) through (6): ##STR7##

In the formulae above (2) through (6):

R⁴ and R⁵ are independently selected from hydrogen, C₁ -C₁₂ -alkyl or C₁-C₁₂ -alkoxy.

R⁶ and R⁷ are independently selected from C₁ -C₁₂ -alkyl or C₁ -C₁₂-alkoxy.

In all formulae (2) through (6), at least two of the groups X¹ to X⁴ arepreferably halogen (preferably chlorine), nitro or nitrile, with nitrilegroups especially preferred. According to another preferred embodimentone of the benzol rings of the compounds of formulae (2) through (6)carries two halogen atoms, nitro groups or (preferably) nitrile groups.

It is also preferable in the formulae (2) through (5) that one of thebridges, Z¹, Z², Z³ in each formula be carboxyl (--COO--) or oxycarbonyl(--OOC--) and the other one be a simple covalent bond.

There is at most one carboxyl or oxycarbonyl bridge in the molecule.

The "compounds (1)" can be obtained by known methods, for example, bycondensation of corresponding phenols or cyclohexanols with thecorresponding benzoic acids or cyclohexane carbon acid combinations.Where the respective acid components are used, preferably in the form ofa corresponding reactive functional acid derivative, e.g., an acidhalide, particularly the acid chloride, the reaction is carried out in afluid organic base, such as, pyridine.

LC-compositions according to the invention contain as components a"compound (1)", e.g., in weight percentage proportions of 1-40, orseveral varying "compounds (1)" in even larger proportions if desired.LC-compositions are preferred which contain as components at least onecompound of the formulae (2) through (6) above.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

EXAMPLE 1 Production of2-cyano-4-n-butylphenyl-(4"-n-pentyl-trans-cyclo-hexyl-4'-trans-cyclohexanoate

(Formulae 2: R⁴ =n--C₅ H₁₁ --, Z³ =--, Z¹ =--COO--, X¹ =--CN, R⁵ =n--C₄H₉ --). 4-trans-(4'-trans-n-pentylcyclohexyl)-cyclohexane carbon acid (7g, 25 mM) was heated with thionylchloride (40 ml) for 30 minutes atbackflow temperature. The resulting acid chloride was separated from thesupernatant thionyl chloride. The acid chloride thus obtained was thentrickled into a solution of 2-cyano-4-n-butylphenol (4.5 g, 25 mM) in100 ml of pyridine at 0° C. After the reaction was finished the mixturewas poured into supernatant thinned hydrochloric acid and extracted withmethylene chloride. The raw product obtained from the extract by boilingit down was recrystallized from hexane. The target combination of thisexample obtained in this manner is nematic-enantiotrope (T_(m) =66.1°C., T_(c) =157.8° C.) and has a negative DC-anisotropy as well as aΔn≦0.2.

EXAMPLE 2 Production of2,3-dichloro-4-n-pentylphenyl-(4"-n-pentyl-transcyclohexyl-4')-trans-cyclohexanoate

(Formula 2: R⁴ =n--C₅ H₁₁, Z³ =--, Z¹ =--COO--, X¹ =Cl, X² =Cl, R⁵=n--C₅ H₁₁). 4-trans-(4'-trans-n-pentylcyclohexyl)-cyclohexane carbonacid (10 g, 36.5 mM) was boiled under reflux with thionylchloride (50ml) for one hour. The supernatant thionylchloride was distilled. Theresulting acid chloride was trickled into a solution of 5.3 g (36.5 mM)of 2,3-dichloro-4-n-pentylphenol (6p 85° C./0.007 torr) in 100 ml ofpyridine. The reaction mixture was stirred over night and then pouredonto thinned hydrochloric acid. The product was extracted with methylenechloride. To purify it the product was recrystallized from hexane. Itshows an enantiotropic nematic phase (Tm=40° C., Tc=180° C.) and has anegative DC-anisotropy as well as a Δn≦0.2.

EXAMPLE 3 Production of2,3-dicyano-4-n-pentylphenyl-(4"-n-pentyl-trans-cyclo-hexyl-4')-trans-cyclohexanonate

(Formula 2: R⁴ =n--C₅ H₁₁, Z³ =--, Z¹ =--COO--, X¹ =CN, X² =CN, R⁵=n--C₅ H₁₁).

According to the procedure described in Example 2, the compound of thepresent example was produced in an analogous manner from equimolar (36.5mM) amounts of cyclohexane carbon acid compound of Example 2--again byconverting the same with thionylchloride into the corresponding acidchloride--and, 2,3-dicyano-4-n-pentylphenol (instead of thecorresponding dichlorophenol of Example 2), and worked up in the samemanner as above. The compound thus obtained is alsonematic-enantiotropic and has a negative DC-anisotropy as well as aΔn≦0.2.

EXAMPLES 4-20

The following anisotropic "compounds (1)" also having a negativeDC-anisotropy according to the invention were produced in a mannersimilar to that above. The cyclohexyl rings are respectively intrans-configuration: Δn≦0.2.

EXAMPLE

4: 2,3-dicyano-4-propylphenyl-(4"-propyl-p-phenylene-4')-cyclohexanoate.

5: 2,3-dicyano-4-propylphenyl-(4"-pentyl-p-phenylene-4')-cyclohexanoate.

6:2,3-dicyano-4-propylphenyl-(2",3"-dicyano-4"-propyl-p-phenylene-4')-cyclohexanoate.

7:2,3-dicyano-4-propylphenyl-(3"-cyano-4"-propyl-p-phenylene-4')-cyclohexanoate.

8:2,3-dichloro-4-pentylphenyl-(4"-propyl-p-phenylene-4')-cyclohexanoate.

9:2,3-dichloro-4-pentylphenyl-(3"-cyano-4"-propyl-p-phenylene-4')-cyclohexanoate.

10: 2,3-dicyano-4-propylphenyl-(4"-pentylcyclohexyl-4')-cyclohexanoate.

11: 2,3-dicyano-4-pentylphenyl-(4"-pentylcyclohexyl-4')-cyclohexanoate.

12: 2,3-dichloro-4-propylphenyl-(4"-pentylcyclohexyl-4')-cyclohexanoate.

13: 2-cyano-4-propylphenyl-(4"-pentylcyclohexyl-4')-cyclohexanoate.

14: 2-cyano-4-pentylphenyl-(4"-pentylcyclohexyl-4')-cyclohexanoate.

15: 2-chloro-4-pentylphenyl-(4"-pentylcyclohexyl-4')-cyclohexanoate.

16: 2-nitro-4-pentylphenyl-(4"-pentylcyclohexyl-4')-cyclohexanoate.

17: 2-cyano-4-propylphenyl-(4"-pentylcyclohexyl-4')-2'-cyanobenzoate.

18: 2-cyano-4-propylphenyl-(4"-pentylcyclohexyl-4')-3'-cyanobenzoate.

19:2-cyano-4-propylphenyl-(2"-cyano-4"-pentylphenylene-4')-cyclohexanoate.

20:2-cyano-4-propylphenyl-(3"-cyano-4"-pentylphenylene-4')-cyclohexanoate.

EXAMPLES 21-38

The following compounds of formula (6) above according to the inventionare anisotropic and show a negative DC-anisotropy and a Δn≦0.2.

EXAMPLE

21: 4-propylcyclohexyl-4'-propyl-2',3'-dicyanobenzoate.

22: 4-propylcyclohexyl-4'-pentyl-2',3'-dicyanobenzoate.

23: 2,3-dicyano-4-propylphenyl-4'-heptycyclohexanoate.

24: 2,3-dicyano-4-pentylphenyl-4'-propylcyclohexanoate.

25: 2,3-dicyano-4-pentylphenyl-4'-pentylcyclohexanoate.

26: 2,3-dichloro-4-propylphenyl-4'-propyloxycyclohexanoate.

27: 2,3-dibromo-4-pentylphenyl-4'-propoxycyclohexanoate.

28: 2,3-dinitro-4-pentylphenyl-4'-pentyloxycyclohexanoate.

29: 2,3-dicyano-4-propylphenyl-4'-propylcyclohexane.

30: 2,3-dicyano-4-propylphenyl-4'-pentylcyclohexane.

31: 2,3-dicyano-4-propylphenyl-4'-heptylcyclohexane.

32: 2,3-dicyano-4-pentyloxyphenyl-4'-propoxycyclohexane.

33: 2,3-dicyano-4-pentyloxyphenyl-4'-pentyloxycyclohexane.

34: 2,3-dicyano-4-propylphenyl-4'-butoxycyclohexane.

35: 2,3-dichloro-4-pentylphenyl-4'-propylcyclohexane.

36: 2,3-dinitro-4-heptylphenyl-4'-propylcyclohexane.

37: 2,3-dichloro-4-pentylphenyl-4'-butoxycyclohexane.

38: 2,3-dinitro-4-pentylphenyl-4'-butoxycyclohexane.

All compounds of Examples 1 to 38 also have advantageously low Δn<0.2and the cyclo-hexane rings are respectively in trans-configuration. Thecompounds (1) according to the invention have the surprising, additionaladvantage that their γ-values (γ=(Δε/ε)) are small and often amount toabout 2 at the most, i.e., γ≦2.

Having now fully described this invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit or scope of the inventionset forth herein.

What is claimed as new and intended to be covered by Letters Patentis:
 1. An anisotropic compound with negative or positive DC-anisotropyand an optical anisotropy Δn≦0.2 having the formula (1): ##STR8## inwhich R¹ and R² are independently hydrogen, alkyl having 1 to 12 carbonatoms, alkoxy having 1 to 12 carbon atoms or one of R¹ and R² canrepresent a cyclical fragment of formulae (1a) or (1b): ##STR9## whereinone of the bridges Z¹, Z² and Z³ in each formula is carboxyl oroxycarbonyl and the other, when present, is a covalent bond, R³ ishydrogen, alkyl of 1 to 12 carbon atoms or alkoxy of 1 to 12 carbonatoms, and X¹ to X⁴ are independently hydrogen, halogen, nitrile ornitro, wherein at least two of X¹ to X⁴ are not hydrogen.
 2. Thecompound of claim 1, having the formula (2): ##STR10## wherein R⁴ and R⁵are hydrogen, alkyl or alkoxy groups having 1 to 12 carbon atoms,respectively.
 3. The compound of claim 1, having the formula (3):##STR11## wherein R⁴ and R⁵ are hydrogen, alkyl or alkoxy groups having1 to 12 carbon atoms, respectively.
 4. The compound of claim 1, havingthe formula (4): ##STR12## wherein R⁴ and R⁵ are hydrogen, alkyl oralkoxy groups having 1 to 12 carbon atoms, respectively.
 5. The compoundof claim 1, having the formula (5): ##STR13## wherein R⁴ and R⁵ arehydrogen, alkyl or alkoxy groups having 1 to 12 carbon atoms,respectively.
 6. The compound of claim 1, having the formula (6):##STR14## wherein R⁶ and R⁷ are alkyl or alkoxy groups having 1 to 12carbon atoms, respectively.
 7. The compound of claim 1, 2, 3, 4, 5 or 6,wherein both X¹ and X² are halogen, nitro or nitrile.
 8. A liquidcrystal composition which comprises at least two components at least oneof which is an anisotropic compound with negative or positiveDC-anisotropy and an optical anisotropy Δn≦0.2, having the formula (1):##STR15## in which R¹ and R² are independently hydrogen, alkyl having 1to 12 carbon atoms, alkoxy having 1 to 12 carbon atoms or one of R¹ andR² can represent a cyclical fragment of formula (1a) or (1b): ##STR16##wherein one of the bridges Z¹, Z² and Z³ in each formula is carboxyl oroxycarbonyl and the other, when present, is a covalent bond, R³ ishydrogen, alkyl of 1 to 12 carbon atoms or alkoxy of 1 to 12 carbonatoms, and X¹ to X⁴ are independently hydrogen, halogenn, nitrile ornitro, wherein at least two of X¹ to X⁴ are not hydrogen.
 9. The liquidcrystal composition of claim 8, wherein the anisotropic compound has theformula (2): ##STR17## wherein R⁴ and R⁵ are hydrogen, alkyl or alkoxygroups having 1 to 12 carbon atoms, respectively.
 10. The liquid crystalcomposition of claim 8, wherein the anisotropic compound has the formula(3): ##STR18## wherein R⁴ and R⁵ are hydrogen, alkyl or alkoxy groupshaving 1 to 12 carbon atoms, respectively.
 11. The liquid crystalcomposition of claim 8, wherein the anisotropic compound has the formula(4): ##STR19## wherein R⁴ and R⁵ are hydrogen, alkyl or alkoxy groupshaving 1 to 12 carbon atoms, respectively.
 12. The liquid crystalcomposition of claim 8, wherein the anisotropic compound has the formula(5): ##STR20## wherein R⁴ and R⁵ are hydrogen, alkyl or alkoxy groupshaving 1 to 12 carbon atoms, respectively.
 13. The liquid crystalcomposition of claim 8, wherein the anisotropic compound has the formula(6): ##STR21## wherein R⁶ and R⁷ are alkyl or alkoxy having 1 to 12carbon atoms, respectively.
 14. The liquid crystal composition of claim8, 9, 10, 11, 12 or 13, wherein both X¹ and X² are halogen, nitro ornitrile.
 15. The compound of claim 1, 2, 3, 4 or 5 where each of R¹, R²,R³, R⁴, and R⁵ when present in the compound is alkyl having 1 to 12carbon atoms.